Section 6-1 “Chromosomes & Meiosis”

Biology Essential Question: At the end of this section you will need to be able to answer this question … How does a gamete differ from a body cell? Why does a gamete have only half the number of chromosomes as a body cell?

KEY CONCEPT You have body cells (somatic cells) and gametes.

Cells in your body can be divided into two types: somatic cells and germ cells.  Somatic cells (BODY CELLS) – make up most of your tissues and organs. (Not passed on to offspring) Examples: brain cells, kidney, eyeballs, skin body cells

Cells in your body can be divided into two types: somatic cells and germ cells.  Germ cells- cells that make up your reproductive organs  Gametes - sex cells also called germ cells – ova (eggs) in female and spermatozoa (sperm cells) in male. This DNA is what is passed on to your children (offspring) sex cells (sperm) sex cells (egg)

Which of the cells below are somatic cells? Which would be gametes? Egg Cells Sperm Cells Muscle Cells Nerve Cells Rod Cells Hair Cells

Chromosome and Meiosis Power Notes List 3 facts about Somatic Cells List 2 facts about Gametes Somatic Cells Gametes Body cells Make up tissues and organs Not passed on to offspring Sex cells Passed on to offspring

Chromosome - a grouping of coiled strands of DNA, containing many genes.

Chromosome number does not seem to be related to the complexity of an organism Yeast: 32 chromosomes – (16 pairs) Fruit flies: 8 chromosomes - (4 pairs) Indian Fern: 1248- (624 pairs) Humans: 46 chromosomes – (23 pairs)

Your cells have autosomes and sex chromosomes The human cell has 46 chromosomes, which are in pairs. --23 pairs. Chromosomes are large DNA structures made up of many genes. These 23 pairs encode you, 23 came from your father and 23 from your mother, and each gave you one of each pair.

Each pair of chromosomes are referred to as homologous pair. Homologous chromosomes are 2 chromosomes (pairs) one from mother and one from father. These chromosomes have copies of the same genes (although the 2 copies may differ – both may be the genes for eyes but one form mother may be for brown and the one for father blue)   The homologous pairs are numbered 1 -23 from largest to smallest. The first 1-22 make up the autosomes.

Homologous chromosomes are pairs of chromosomes have genes for the same traits

The first 22 pairs of chromosomes are autosomes Autosomes contain genes that are not directly related to the sex of the organism

Sex Chromosomes (23rd pair in humans) relate directly to the development of sexual characterisitics. Humans have very different sex chromosomes X and Y

Chromosomes that contain genes not directly related to sex of organisms Homologous Chromosomes pairs, one from each parent Sex Chromosomes that contain a gene that is directly related to sex of organisms

Body cells are diploid; gametes are haploid. Sexual Reproduction = the fusion of two gametes that result in an offspring that are a genetic mixture of both parents. Fertilization: the actual fusion of an egg and sperm. When fertilization occurs, the nuclei of the egg and sperm cell fuse to form one nucleus. This nucleus needs the correct number of chromosomes so the egg and sperm each must contain half – one chromosome form each homologous pair.

Diploid - (2n) cells have two copies of every chromosome Body cells are diploid Half the chromosomes come from each parent

Haploid (n) cells have one copy of every chromosome Gametes (sex cells) are haploid Gametes have 22 autosomes and 1 sex chromosome

Fertilization: When the egg and sperm cell unite 2 haploid cells unite to form a cell (zygote) that once again has the diploid number of chromosomes Chromosome number must be maintained in animals Many plants have more than two copies of each chromosome A zygote fertilized egg cell that grows to be a human

Mitosis makes more identical diploid cells

Meiosis makes haploid cells from diploid cells and: occurs in sex cells produces gametes

Has two copies of each chromosome – one from each parent Body Cells Result of mitosis Has 1 of each chromosome Gamete (sex cell) Result of MEIOSIS

How are Mitosis and Meiosis similar? Mitosis and Meiosis are both types of cell division They both involve the DNA coiling up to make chromosomes The nucleus divides in both processes using many different steps

Creates genetically unique cells Haploid cells Takes place at only certain times in life cycle Sexual reproduction Create identical cells Make diploid cells Happens throughout organisms life time

How are mitosis and meiosis alike? Both involve division of the nucleus followed by the formation of new cells.

Mitosis Meiosis identical / unique diploid / haploid, asexual / sexual What word pairs in the accompanying descriptions of mitosis and meiosis point to the differences between the two types of division? identical / unique diploid / haploid, asexual / sexual Mitosis Meiosis